The present invention relates to a sealing arrangement having two machine parts which are moved relative to one another axially and/or in a rotary movement, and which enclose a sealing ring between concentric sealing surfaces. This ring is composed of an elastic material and has a retaining part positioned radially internally, a sealing part positioned radially externally, and a resilient connecting part joining these two. The retaining part provides a static seal against the inner machine part, and fits under prestressing against the inner sealing surface, which will also be called the base sealing surface hereafter. To cause prestressing, the inner diameter of the retaining part is smaller than that of the base sealing surface. The sealing part is applied under prestressing against the outer opposing sealing surface, which is movable with respect to the sealing part. The retaining part and sealing part essentially lie in the same radial plane. In general, the sealing ring is mounted in a retaining groove in the inner machine part.
Known sealing arrangements of this kind (e.g., U.S. Pat. No. 4,611,931; the present applicant's "Airzet Gasket" brochure) achieve resilience of the connecting part in combination with a single-piece configuration of the sealing ring by having two groove-shaped notches radially offset from one another, which create a Z-shaped profile between the retaining part and the sealing part. Consequently the pressure to be sealed off, being present in one of these grooves, is exerted against the back of the sealing part and thus increases the sealing compression proportionally to the pressure that is to be sealed off. In order that the pressure to be sealed off may reach this groove, the front faces of the sealing part have protrusions or cross-sectional areas of passage that prevent the full surface of the sealing part from being applied like a barrier against the walls of the groove receiving the sealing ring. The proportionality between the sealing compression and the pressure to be sealed off makes it possible to keep the initial prestressing on the sealing part low, thus also keeping static friction (the "slip-stick effect") low. All the same, a certain initial sealing compression must be present and is achieved by elastic prestressing. In known sealing arrangements, this prestressing is accomplished in that the circumferential surface of the sealing part intended to be applied against the opposing sealing surface is given a diameter somewhat greater than the diameter of the opposing sealing surface. Consequently, after installation, the sealing part is crushed in the circumferential direction. Thus the sealing part tends to assume a serpentine shape within the groove holding the sealing ring. Hence the relative position of the sealing part, as viewed in a longitudinal section, is not uniform at all points of the circumference, and therefore the sealing effect is also variable and to some extent less than optimum. Since the prestressing of the sealing part must be great enough to guarantee a tight seal even at those points where the conditions for such tightness are least favorable, the prestressing must be greater than would be necessary if the sealing part had an optimum orientation everywhere.
A known wiper ring (German Patent U-8704249) is composed of a radially internal retaining part, a radially external wiper, and a resilient connecting part joining these parts. The wiper has a lip that performs the wiping function and also, if necessary, sealing functions, and for this purpose is prestressed against the opposing sealing surface by being deformed to a diameter less than its diameter in the unstressed state. So that this lip remains in the correct position with respect to the opposing sealing surface during operation, the wiper is additionally provided with a guide ring whose cylindrical circumferential surface has the same diameter as the opposing sealing surface and rests against the latter surface. Since such a support ring generates additional friction against the opposing sealing surface, it is not applicable for sealing rings that are intended to have a low initial friction against the opposing sealing surface.